What is "slumbercoach"

The Slumbercoach is an 85-foot-long, 24 single room, eight double room streamlined sleeping car. Built in 1956 by the Budd Company for the Chicago, Burlington and Quincy Railroad for service on the Denver Zephyr, subsequent orders were placed in 1958 and 1959 by the Baltimore and Ohio Railroad and Missouri Pacific Railroad for the Texas Eagle/ National Limited, then in 1959 by the Northern Pacific Railway for its North Coast Limited and also the New York Central Railroad for use on the 20th Century Limited.